The 3GPP (3rd Generation Partnership Project) launched LTE (Long Term Evolution) in 2005, which aims to provide support for increasing requirements from operators and subscribers with higher data throughput and better network performance.
The 3GPP R6 has introduced High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA). The primary design target for a wireless communication system is packet field service to support highly real-time service and reduce delay in wireless network. The current criterion is derived with reference mainly to Quality of Services (QoS) of various real-time services, such as Voice over IP (VoIP) and the like. Meanwhile, status transition delay of a control plane in the system is reduced, which is helpful to improve users' experience of network services. The air unidirectional delay is less than 5 ms in the user data plane, and the delay for a user transiting from an idle status to a connection status is less than 100 ms in the control plane. The 3GPP evolution involves technical standards of CDMA2000, WCDMA (Wideband Code Division Multiple Accesses) and LTE.
FIG. 1 shows schematically a mobile communication network by example of a LTE system. As shown in FIG. 1, in the mobile communication network, a plurality of base stations (NodeBs) are connected with a core network gateway (MME/UPE). One core network gateway manages several NodeB nodes. Each of the plurality of base stations can adapt more than one mobile station (i.e., User Equipment, UE), and each mobile station can always perform transmission/reception to/from the respective base station by using a dedicated channel (Dedicated Physical Control Channel, DPCCH). Further, the mobile stations in the mobile communication network can perform data reception with HSDPA and data transmission with EUDCH (Enhanced Uplink Dedicated Channel). The base stations conduct schedule based on these packet transmission systems, and allocate radio resources to the respective mobile stations for communication with the mobile stations.
In order to achieve an error-free data transmission, the error control strategy adopted in LTE is still Hybrid ARQ (HARQ) obtained from a combination of FEC (Forward Error Coding) and ARQ. HARQ utilizes a retransmission strategy of Increment Redundancy (IR). Retransmission serves as an approach to error correction in the data link layer of mobile communication, and HARQ has a good performance in this respect.
To improve system performance, HSUPA adopts the technique HARQ at the physical layer and supports two types of combining mechanisms, i.e., Chase Combining (CC) of the same packets retransmitted from a base station and IR Combining of packets containing different information (i.e., redundant information) retransmitted from a base station. Information is transmitted directly between UE and NodeB in a fashion of ACK/NACK, in which the receiving side will send ACK information to the transmitting side over a respective channel if it receives data correctly, otherwise, it will send NACK information. This facilitates the transmitting side to learn whether a retransmission is needed in an accurate and timely way.
In current phase, LTE uplink transmission has the following characters:
1. The 3GPP RAN 1 work group has determined not to use any data-associated signaling in uplink transmission;
2. Synchronized HARQ is adopted in LTE uplink transmission;
3. It has been proposed now that a common Maximum HARQ retransmission number is applied for all radio bearers;
4. The 3GPP has now specified that adaptive HARQ can be used for uplink transmission; and
5. The downlink signaling overhead should be minimized to increase the system capacity.
In HSUPA, the data-associated signaling, RAN=0, is used in the uplink to indicate to eNodeB (base station) that the mobile station is now performing new data transmission, which aims to ensure a correct HARQ combination by the eNodeB, so that the base station can determine, based on the quality of received signals, whether the mobile station will conduct new data transmission or data retransmission in the next step. In LTE, however, the RAN 1 work group has determined not to use any data-associated signaling in uplink transmission. As a result, the mobile station (UE) cannot notify the eNodeB whether it is conducting a new data transmission or data retransmission. It is thus impossible to ensure a correct HARQ combination by the eNodeB.
In HSUPA, the data-associated signaling is used in the uplink to indicate a new data transmission, for example, notifying the receiving side how the data are transmitted via signaling. The receiving side can demodulate the data using a corresponding method. Unfortunately, the prior art strategy cannot be applied in LTE since the use of any data-associated signaling is not allowed in LTE uplink. Occasions may occur that the receiving side (base station) is not aware that the transmitting side (UE) has begun to transmit new data and still waits for retransmission of previous data from the transmitting side. To keep synchronization between the transmitting and receiving sides in a certain fashion, the receiving side shall learn whether the transmitting side is transmitting new data or retransmitting data.